The present invention relates to crescent-shaped beam-like parts, such as brake shoes, and further relates to apparatus and methods for manufacturing the same.
Existing drum-type brake systems for passenger vehicles include a brake shoe assembly comprising a brake shoe and a brake pad configured to operate with other components for braking and stopping a vehicle. Drum-type brake shoe assemblies are well known in the art, and need not be described herein. These brake shoes typically include a pair of stamped parts welded together to form a center web and a rim that extends about 160 to 170 degrees around the center web to define a semi-cylindrical shape corresponding to a brake pad for supporting the brake pad against an interior cylindrical surface of a brake drum. The center web and the rim form a T-shaped beam-like cross-section that is structurally sufficient to endure the radial and nonradial forces and abuse encountered in use, and further, the center web includes multiple holes, apertures, and notches that facilitate its use with the other vehicle components of the vehicle braking system. Historically, the brake shoes are made by a combination of multiple steps of stamping and welding. However, manufacturing methods and apparatus are desired for manufacturing brake shoes faster, more efficiently, at lower cost, and more consistently. Further, improvements in brake shoes are desired that permit lighter weight brake shoes to be made without resorting to expensive high-strength materials. Also, improvements in brake shoes are desired that can be more easily arcuately bent or swept into a dimensionally-accurate arcuate shape, yet that are sufficiently strong for use as a brake shoe.
Brake shoes made using rollforming technology have been proposed, but such designs to date have been dismissed by persons skilled in the art of rollforming as not commercially feasible. One reason, discussed in more detail below, is because it is very difficult to consistently and reliably bend a T-shaped beam section made from materials having the proposed strength and thickness (e.g. steel sheet having a strength of 60 KSI and a thickness of about 4 mm) into an arcuate shape with sufficient accuracy and repeatability to meet manufacturing specifications for brake shoes. Yet, in order to take maximum advantage of rollforming, the T-shaped beam must first be rollformed, and then the beam must be swept against the xe2x80x9cstrengthxe2x80x9d of the beam into a very accurate arcuate shape and then cut to length.
One feature that complicates the manufacture of brake shoes is that they have tight dimensional requirements, and further, the brake shoes have a very small radius, such as about 100 mm radius to an outer surface of the brake shoe. The reasons for the need for tight dimensional requirements are many, but include such things as the need for reliability and consistency of vehicle brakes and the braking operation (including uniform support for all portions of a brake pad), safety, long service life, liability for braking malfunction, and governmental standards. A problem with sweeping or bending of a T-shaped beam is that it causes the beam to xe2x80x9csnakexe2x80x9d or wander longitudinally as the beam is bent, and further causes the beam flanges to undulate and bend in uncontrolled ways as some beam material is compressed and other beam material is stretched. xe2x80x9cSnakingxe2x80x9d and non-uniformity is especially problematic on the rim flanges of a brake shoe because the rim flanges must uniformly support a brake pad for good braking performance. Further, the smaller the radius of the bend, the more difficult it is to eliminate snaking and objectionable non-uniformity. Also, good uniformity and xe2x80x9cnon-undulationxe2x80x9d of beam flanges is important to good beam strength, because non-uniformities and undulations can result in premature buckling, bending, and distortion problems. xe2x80x9cSnakingxe2x80x9d and non-uniformity is also problematic on the center web, since the material of the center web is bent from a linear planar shape to a crescent planar shape while trying to keep the material in the same plane. The problems of snaking and undulations can increase as material thickness and strength are increased.
Another problem occurs when the entire brake shoe is made from a single sheet, instead of being made from separately formed opposing halves that are welded together. The entire brake shoe should preferably be made from a single sheet in order to take maximum advantage of rollforming technology, since this eliminates the need to weld separate pieces together. But in order to make a brake shoe from a single sheet, the center web of the brake shoe must be formed by doubling over adjacent wall sections. When doubled over, the adjacent wall sections are connected by a sharply-bent inner edge. Depending on the material, the sharply-bent inner edge will often split, either at the time it is bent into the doubled back condition or it will split at a later time when in service and during use. In particular, the thick and strong materials needed for manufacturing brake shoes may tend to fracture and break when sharply bent over to form a double thickness wall.
The present invention solves the aforementioned problems and includes aspects having the aforementioned desired advantages.
One aspect of the present invention is to provide an apparatus adapted to form a plurality of arcuately-shaped beam sections, such as brake shoes, from sheet material. The apparatus includes a rollformer, a cut-off device, and a sweeping device. The rollformer includes rollers constructed and arranged to rollform the sheet material into an elongated T-shaped beam that includes a center web and a support flange along an edge of the center web. The cut-off device cuts the beam into segments having a predetermined length. The sweeping device is constructed to form the segments into an arcuate longitudinal shape where the support flange is accurately re-formed into a cylindrically-shaped rim having a diameter larger than the center web.
In a narrower form, the rim has an outer surface with all portions being within about 1 mm of a true cylindrical surface. In another narrower form, the beam sections define a radius of less than about 500 mm and in a still narrower form, the beam sections define a radius of less than about 80 to 100 mm or less (depending on functional criteria such as uniformity). Also in yet another narrower form, the cut-off device is constructed to cut the beam sections into lengths of about 400 mm or less.
It is an object of the present invention to provide an apparatus that will rollform sheet material into a brake shoe. The apparatus can easily and quickly form a high-strength brake shoe, and is efficient in use, economical to manufacture, capable of a long operable life, and particularly adapted for the proposed use.